题解 | 牛牛学数列6

import sys

for line in sys.stdin:
    a = int(line.split()[0])

list_a = [0, 1, 1]

if a == 1:
    print(list_a[0])
elif a == 2 or a == 3:
    print(list_a[1])
elif a >= 4:
    for i in range(4, a + 1):
        contents = list_a[i - 4] + 2 * list_a[i - 3] + list_a[i - 2]
        list_a.append(contents)
    print(list_a[a - 1])
else:
    print("请输入正整数")